The process of DNA replication is the primary target of anticancer chemotherapy, since cancer cells, like normal cells, have to replicate their DNA in order to divide. Identification of the proteins that are needed for DNA replication can provide new candidates against which to design novel anti-tumor drugs. To date, most anticancer drugs have been directed against the enzymatic machinery of DNA synthesis. However, the genetic mutations that lead to cancer are rarely found in these enzymes. Instead, it is the genes involved in signaling pathways controlling the initiation of DNA synthesis during the cell cycle origin responding to errors of replication that are most often mutated in cancer cells.
Chromosomal replication origins are molecular switches, where the major regulated step of DNA synthesis, the initiation of replication, occurs. The applicants previously identified the origin of replication of the human c-myc gene. Characterization of the c-myc origin has led to the discovery of a new protein, called DNA Unwinding Element binding protein (DUE-B) that binds in vivo in a yeast one-hybrid assay to an important control site in the c-myc origin, the DNA unwinding element (DUE).
Other relevant protein complexes are known in the art. For instance, U.S. Pat. No. 5,217,864 describes a replication initiator protein complex for eukaryotic cells that comprises a purified protein complex capable of origin-specific DNA binding in vitro. While this protein has not been shown to function as such in vivo, it may be useful in the development of specific diagnostic and therapeutic applications, such as drug assays to identify inhibitors of S phase initiation.
However, no protein has been identified to date with the property of binding in vivo to a region of DNA that controls DNA replication. Accordingly, the need remains in the art for new ways to interfere with the cell division cycle.
It would therefore be desirable to identify a novel DNA binding protein for use as a target in pharmaceutical assays for chemotherapeutic drugs designed to inhibit tumor cell division, as well as to identify other compounds effective in enhancing or retarding cell division.
It would also be desirable to prepare antibodies or antibody derivatives that react with the DNA binding protein.
It would further be desirable to prepare cloned and purified forms of the DNA binding protein from bacterial and eukaryotic cells, as well as modified forms of such a protein fused or not to other polypeptides.